Jeanette — I do see parallels to Zusne and Jones’s description of collective hallucination and persisting notions of Multiple Personality Disorder, particularly in the “therapeutic” technique of “recovered memory” treatment. Recovered Memory Therapies have proven to be a sometimes subtle (sometimes not as much) “harmonizing of accounts” between the therapist, bent upon surfacing a presumably repressed trauma, and the client who, once subscribing to the therapist’s account, feels compelled to make it fit. Confirmation bias is flagrantly encouraged in this process, and bad dreams, negative thoughts, virtually any flaw imaginable is seen as evidence of repression.
While the Fatima observer might mold the memory of retinal distortion into a distinct image of a dancing sun, so the recovered memory therapy client molds broken images of childhood — which have been “therapeutically” contextualized for her as a root of fear, phobia, neurosis, and depression — into images of abuse. Specialists in Dissociative Identity Disorder stir up a panic and then yell “Lo! In the sky!” for a living.
As Altus points out, all it takes is somebody with a vision (or delusion, or demetia) and a few “experts” in the right environment. Of course, the time was ripe at the beginning of the Multiple Personality/Satanic Panic fraud, with a perfect storm of conservative religious interests intersecting with those of some feminists and finding common ground in amplified fears of religious cults and a growing daycare culture.

You know I really never thought of this. Excellent critical debunking of the notion of “mass hallucination.”

I have thought for some time that belief systems are only as successful as the host culture they are being introduced into is receptive. You didn’t have Pentecostalism catching fire in Germany but it took off like wildfire in rural Latin American where mythical beliefs flourished. It’s like heath, a virus is often only as strong as its host is weak. What I didn’t think of was how small the spark need be—someone with a vision, a few “experts” on the subject. When the culture is receptive, you don’t need and as you point out, two or more people getting their delusions from some shared supernatural event, which seems, given the nature of the brain to be impossible, just some people who are inclined to believe the myth, through shared information/bias, perhaps followed by a second wave willing to suspend their disbelief and before you know, the masses have come to believe.

You leave me wondering if “global scale mass hallucination or hysteria” can also be attributed to thoughts as we see in the collective agreement to believe in the existence of multiple personalities/alter selves?

In the examples you highlight, could not the “destination” be the office of a psychotherapist? Surely that is where those who thought, or believed, in multiple selves flocked.